Calendar management: create, rename, delete, share

[SashankBhamidi]

The client can list calendars. It can't create, edit, delete, or share them.

Add to the client:

create_calendar(name, color=None, timezone=None) -> str
update_calendar(calendar_id, name=None, color=None, timezone=None)
delete_calendar(calendar_id)
share_calendar(calendar_id, account_id, rights)
get_calendar_subscriptions() -> list
set_default_alerts(calendar_id, alerts)

All use Calendar/set. The existing build_calendar_get / parse_calendar_get in _methods/calendar.py is the pattern. Add build_calendar_set and parse_calendar_set alongside.

Sharing uses shareWith on the Calendar object: a dict of account ID to right strings (mayReadItems, mayWriteAll, etc.).

• Unit tests with mocked responses for each method
• Integration test against Cyrus (sharing needs two test accounts, check if the Docker setup supports it)
• Document what Cyrus and Stalwart do on delete-with-events